module Liquid

  # Templates are central to liquid. 
  # Interpretating templates is a two step process. First you compile the 
  # source code you got. During compile time some extensive error checking is performed. 
  # your code should expect to get some SyntaxErrors. 
  #
  # After you have a compiled template you can then <tt>render</tt> it. 
  # You can use a compiled template over and over again and keep it cached. 
  #
  # Example: 
  #   
  #   template = Liquid::Template.parse(source)
  #   template.render('user_name' => 'bob')
  #
  class Template
    attr_accessor :root
    @@file_system = BlankFileSystem.new
    
    class <<self
      def file_system
        @@file_system
      end
    
      def file_system=(obj)
        @@file_system = obj
      end
          
      def register_tag(name, klass)      
        tags[name.to_s] = klass
      end                        
    
      def tags
        @tags ||= {}
      end
        
      # Pass a module with filter methods which should be available 
      # to all liquid views. Good for registering the standard library
      def register_filter(mod)      
        Strainer.global_filter(mod)
      end                        
            
      # creates a new <tt>Template</tt> object from liquid source code
      def parse(source)
        template = Template.new
        template.parse(source)
        template
      end                           
    end

    # creates a new <tt>Template</tt> from an array of tokens. Use <tt>Template.parse</tt> instead
    def initialize
    end
    
    # Parse source code. 
    # Returns self for easy chaining    
    def parse(source)
      @root = Document.new(tokenize(source))
      self
    end
    
    def registers 
      @registers ||= {}
    end
    
    def assigns
      @assigns ||= {}
    end
    
    def errors
      @errors ||= []
    end
        
    # Render takes a hash with local variables.
    #
    # if you use the same filters over and over again consider registering them globally 
    # with <tt>Template.register_filter</tt>
    # 
    # Following options can be passed:
    #  
    #  * <tt>filters</tt> : array with local filters
    #  * <tt>registers</tt> : hash with register variables. Those can be accessed from 
    #    filters and tags and might be useful to integrate liquid more with its host application  
    #
    def render(*args)
      return '' if @root.nil?

      context = case args.first
      when Liquid::Context
        args.shift
      when Hash
        self.assigns.merge!(args.shift)        
        Context.new(assigns, registers, @rethrow_errors)
      when nil
        Context.new(assigns, registers, @rethrow_errors)
      else
        raise ArgumentError, "Expect Hash or Liquid::Context as parameter"
      end
      
      case args.last
      when Hash
        options = args.pop
        
        if options[:registers].is_a?(Hash)
          self.registers.merge!(options[:registers])  
        end

        if options[:filters]
          context.add_filters(options[:filters])
        end
      when Module
        context.add_filters(args.pop)    
      when Array
        context.add_filters(args.pop)            
      end
                              
                              
      # render the nodelist.
      # for performance reasons we get a array back here. to_s will make a string out of it
      begin
        @root.render(context).join
      ensure
        @errors = context.errors
      end
    end
    
    def render!(*args)
      @rethrow_errors = true; render(*args)
    end
       
    private
    
    # Uses the <tt>Liquid::TemplateParser</tt> regexp to tokenize the passed source
    def tokenize(source)      
      return [] if source.to_s.empty?
      tokens = source.split(TemplateParser)

      # removes the rogue empty element at the beginning of the array
      tokens.shift if tokens[0] and tokens[0].empty? 

      tokens
    end
     
  end  
end
